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Research

Our Group develops and applies state-of-the-art methodology, novel when necessary, in order to gain a microscopic quantum-mechanical description of the complex electronic interactions ubiquitous in systems of technological interest. In particular, we specialise in developing electronic structure methods appropriate to larger systems, i.e. at or approaching experimental length-scales, and only those which strike a good compromise between computational tractability and accuracy. We are active developers of the ONETEP linear-scaling DFT code wherein most of our PhD and summer students gain experience in advanced simulaitons and high-performance software development.

We have a long-standing research strand on transition-metal physics and chemistry generally, which is both interesting and challenging for us due to the emergence of strong electronic correlation effects. Our studies in this area have been diverse, ranging from insulating oxides, to strongly-correlated metals and dilute magnetic semiconductors, through to small organometallic dyes and up to biological metalloproteins. The methodology that we develop is very generally applicable to systems spanning a range such as this. We have developed, in collaboration, a comprehensive and sophisticated suite of extensions to the linear-scaling DFT+U code developed during David’s PhD, now including cluster DFT+DMFT including total-energies, a very flexible constrained DFT module, numerous methods for defining subspaces for special treatment based on atomic orbitals or optimised Wannier functions, PAW+U, Pulay forces, and numerous forms of corrective Hamiltonian, including Hund’s exchange.

Increasingly, we are working in the area of theoretical spectroscopy, simulating spectroscopies such as photoemission, optical absorption, and electron energy loss on a routine basis. For this we use theories including TDDFT and many-body perturbation theory within the GW and related approximations. Two slightly more exotic classes of spectra are also receiving active attention, namely chiroptical or magneto-optical spectra and those exhibiting strong non-linear or bosonic coupling effects. At present, we are working actively in the area of corrective approaches to the latter approximations, both for addressing known pathologies and for replacing physical effects lost in their construction.

Specialist technical capabilities of our Group:

  • Large-scale (~10,000 atom) quantum-mechanical simulations including transition-metal and lanthanoid systems
  • Advanced population schemes involving nonorthogonal orbitals, and their propagation and optimisation
  • Calculating Hubbard U and Hund’s J parameters, self-consistently
  • Advanced and flexible constrained DFT, including geometry optimisation
  • Linear-scaling DFT+DMFT for molecular and disordered solid-state systems
  • Pseudopotential generation for more challenging elements
  • Theoretical spectroscopy, experience with codes such as Quantum Espresso, Abinit, Octopus, Yambo, BerkeleyGW etc.
  • Calculation of valence-electron spectra such PES, IPES, UV, ECD, and EELS
  • Simulation of mechanical, surface and interface properties, including finite temperature
  • Ballistic electronic transport calculations, including finite bias effects
  • Calculation of electric dipole moments and polarisabilities, Born effective charges etc. in large nano structures

The kinds of system that we have recently studied (we like to collaborate, please get in touch)

  • Transition and lanthanoid oxides, dioxides, and vanadates
  • Novel two dimensional materials, including phosphorene
  • Transition metal oxide battery cathode materials (charge- and spin-density wave)
  • Nobel metal alloys, interfaces, and surfaces
  • Dilute magnetic semiconductor gallium manganese arsenide
  • Self-assembled AlGaAs quantum dots
  • Organometallic proteins implicated in mammalian respiration
  • Diatomic molecules undergoing dissociation